1. Field of the Invention
The present invention generally relates to a cathode ray tube having a funnel with a reverse curvature, and more particularly, to a cathode ray tube having a funnel with the strength for dealing with internal vacuum and implosion condition by applying a reverse radius to the whole rear-side glass (that is, a “funnel”) of the cathode ray tube. Therefore, the cathode ray tube of the present invention has the strength satisfying the requirement of the glass manufacturing process and test specification of a funnel for a cathode ray tube.
2. Description of the Prior Art
A funnel, which is a funnel for a conventional cathode ray tube (hereinafter, referred to as ‘CRT’), forms an optimum curve by combining various kinds of curves in its design. Recently, it has required that the structure of CRT can shorten the external length of a tube axis direction and accomplish large deflection of electric beams according to scale-up and complanation of the CRT. However, the funnel that satisfies large deflection and narrow CRT has been degraded characteristics of vacuum resistant stress and implosion proof. Accordingly, a funnel is required to have high strength and satisfy large deflection and narrow CRT. In the conventional funnel design, center of curvature up to a yoke portion is located at the outer side of the CRT, while that of a body portion in the funnel on the inner side of the CRT.
Referring to FIG. 1, a recent cathode ray tube has a glass bulb of high vacuum comprising a panel 1 and a funnel 2. The panel 1 is formed of glass displaying image basically. The funnel 2 is formed of glass having a neck portion 5 for receiving an electric gun 6, a yoke portion 4 and a body portion 3. On the yoke portion 4, a deflecting coil 7 is mounted. The body portion 3 extends from the yoke portion 4 toward an opening terminal portion that the panel 1 is attached. Referring to solid lines in FIGS. 1 and 3, curvature r1 of the yoke portion 4 places its center on the outer side of the CRT while curvature r2 of the body portion 3 places its center on the inner side of the CRT. As a result, an inflection point 15 is located between the yoke portion 4 and the body portion 5.
The CRT having the structure as described above can shorten the external length of a tube axis direction and accomplish large deflection of electric beams according to scale-up and complanation of the CRT. However, the strength for preventing implosion of the funnel at the internal vacuum condition of the CRT is attenuated. As the length of the tube axis direction become shorter, the body portion 3 of the funnel becomes relatively wider. As a result, as shown in FIG. 1, the thickness of the body portion 3 becomes thicker, and its stress becomes more increasing. Since this point causes the weight of the CRT to become larger and heavier, it is an important problem in a glass manufacturing process, manipulation and transport of the CRT.
The Japanese Patent Application No. 2000-251766 (published on Sep. 14, 2000) shows an attempt to overcome the above-described problem of the conventional CRT. Referring to FIG. 2, a funnel 2′ includes a protrusion 8′ wherein a body portion 3 around a yoke portion 4 is projected to the outer side side, thereby increasing the vacuum resistant strength and minimizing the increase in thickness of the body portion 3. As a result, the weight of a CRT becomes lighter. In this way, by forming the protrusion 8′, a ring-shaped groove bottom 9 is formed around a yoke portion 4, and a deflecting coil 7 is mounted therebetween.
However, in the above-described Japanese Patent Application, it is difficult to fabricate the funnel 2′ because the structure of the funnel 2′ is complicated. In addition, it is difficult to apply the structure of the conventional deflecting coil 7 and electric gun 6 to the CRT. This application requires new equipment to mount the deflecting coil 7 or the electric gun 6. As a result, its installment becomes difficult.